chore: fix stack's nix integration

The pkgconfig package has been renamed to pkg-config in... February
2019. So this has not been working for quite some time.

Author: wolfgangwalther

stack.yaml

@@ -2,9 +2,8 @@ resolver: lts-22.44 # 2025-05-02, GHC 9.6.7
 
 nix:
   packages:
-    - pcre
-    - pkgconfig
-    - postgresql
+    - libpq
+    - pkg-config
     - zlib
   # disable pure by default so that the test environment can be passed
   pure: false